Download A Legacy Study of Stellar Life Cycles in the Galactic Center

A Legacy Study of Stellar Life Cycles
in the Galactic Center
Franz Bauer (Columbia), Michael Muno (Caltech),
Jon Mauerhan (UCLA), Susan Stolovy, Solange Ramirez (IPAC), Rick Arendt (NASA), Farhad YusefZadeh (Northwestern), Zhongxiang Wang (McGill), Eric Pfahl (KITP), Tetsuya Nagata (Kyoto U.),
Mark Morris (UCLA), Daniel Wang (UMass), Casey Law (Northwestern), Frederick Baganoff (MIT),
Sangwook Park (Penn State), Geoffrey Bower (UCBerkeley), Angela Cotera (SETI), Niel Brandt (Penn
State), Reba Bandyopadhyay (Florida), Cornelia Lang (Iowa), Namir Kassim (NRL), Rudy Wijnands
(Amsterdam), Steve Eikenberry (Florida), Scott Hyman (SBC), Joseph Lazio (NRL)
Wang et al. 2000
Why Return to the Galactic Center?
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Contains 1% of the Galactic stellar mass, and provides a
sample of rare objects:
• Identify transient Low-Mass X-ray binaries.
• Find IR counterparts to High-Mass X-ray binaries (Pfahl et al. 2002)
12 ks
Muno, Bauer et al. in prep
10 pc
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It is the nearest Galactic nucleus:
• Study how in-falling gas is converted to stars in “pseudo-bulges.”
• Search for evidence for past activity of the super massive black
hole, Sgr A*.
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Contains unique features, such as magnetic filaments.
50 ks
The Basic Statistics
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We are sensitive to 1032 erg s-1 (90% conf) over 1 degree2.
We detect nearly 11,000 point sources.
Typical positional uncertainties are 0.5-2”, depending on
offset from aim point.
A Multi-Wavelength Survey
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15, 40 ks Chandra observations supplementing
archival data (up to 1 Msec on Sgr A*).
VLA surveys at 6, 20, and 90 cm (Lang, Yusef-Zadeh,
Kassim, Lazio, et al.).
Spitzer IRAC data (Stolovy, Ramirez, Arendt et al.).
JHKs photometry with SIRIUS on the 1.4m IRSF
(Nagata, Nishiyama et al.).
UKIDSS and VLT photometry (Bandyopadhyay).
Infrared spectroscopy (Mauerhan et al.), eventually
with the Gemini Flamingos II MOS (Eikenberry et al.).
30% X-ray/near-IR (10% real)
300 X-ray/IR (60 GC srcs)
6 X-ray/radio (young * in HII)
10 pc
X-ray Binaries in Outburst
10 pc
Population Synthesis
Observed
Observed as transients
HMXB
LMXB
HMXB
LMXB
HMXB
LMXB
Galactic Center
~10
~10
~3
~17
~1
~16
Galaxy
~1000
~1000
114
185
63
103
X-ray Transients in the Central
Parsec of the Galaxy
• 3 hr/frame (moving avg)
• 6 days 17 hr total
• Lowest color level 15 above
background
• Tail of PWN candidate has ~3
ct/pix, so Poisson statistics causes
apparent variability
• 7 X-ray transients detected
within central 3 pc in past 7 yr
• 4 of 7 detected within central pc
=> 20x overabundant per unit
stellar mass (Muno et al. 2005)
High Mass X-ray Binaries
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Pfahl et al. (2002) predict that there are ~250-600 HMXBs
in the field, and ~50% would be brighter than 1032 erg s-1.
These should have IR counterparts with K=14-19.
10 pc
High Mass X-ray Binaries
698 sources with LX>1032 erg/s
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From our IR photometry, we find that ~3+/-2% of X-ray sources
have counterparts with K<15. So, there are already ~20
candidate HMXBs with LX>1032 erg/s in the field.
UKIDSS will sample much more of the HMXB population (K<17).
X-ray Selected Young Massive Stars
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So far, 16 of 49 stars
we have obtained IR
spectra of are WolfRayet or O stars.
Many show
evidence that they
are binaries.
They are most likely
colliding-wind
binaries.
Mikles et al. (2006), Muno et al. (2006),
Mauerhan et al. (2007, and in prep)
X-rays and Star Formation
Mid-IR: 3.6,4.5,8.0 micron
Star formation is occurring now,
as revealed by HII regions. . .
10 pc
. . . and in the recent past, as
seen from the Arches, Quintuplet,
& central parsec clusters.
Radio: 6,20,90 cm VLA
X-rays and Star Formation
We have identified X-ray emission from the known young stellar
population, and have a more widely-distributed population from
earlier episodes of star formation.
10 pc
X-rays and Star Formation
X-ray: He-like S
10 pc
X-ray: He-like Fe
See also Koyama et al. (2007a,b)
X-rays and Star Formation
Mid IR: 8 micron IRAC
10 pc
Radio: 20 cm VLA
X-rays and Star Formation
Mid IR: 8 micron IRAC
10 pc
Radio: 20 cm VLA
Chandra Galactic Center Deep Field
N
E
17 x 17 arcmin
40 x 40 pc
590 ks
Red: 2-3.7 keV
Green: 3.7-4.5 keV
Blue: 4.5-8 keV
5
pc
Properties of Sgr A*
• Mass ~ 3.7x106 Msun
• Distance ~ 8 kpc
• Quiescent X-ray luminosity ~ 2x1033 erg s-1
(2-10 keV)
• Daily X-ray flares <~ 1035 erg s-1
• Eddington luminosity ~ few x 1044 erg s-1
Chandra Discovery of X-ray Flaring from Sgr A*
(Baganoff et al. 2001)
2000 Oct 27 05:42 UT
45x, 4 hr
ASCA Discovery of Fe Fluorescence
in the Galactic Center
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ASCA is first X-ray satellite launched with
CCD cameras
Discovers Fe Ka fluorescence line (6.3-6.5
keV)
keV) in Sgr B2 molecular cloud (Koyama
et al. 1996)
Equivalent width ~1 keV
Sgr A* upper-limit ~1036 erg s-1 (2-10 keV)
keV)
Time-averaged luminosity required to
produce the line, ~1038 erg s-1, is much
brighter than any nearby X-ray binaries
Size of cloud ~7 pc => light-crossing time
~23 yr
Koyama et al. suggest irradiator might
have been Sgr A*, if it was at least 100x
brighter ~300 years ago
INTEGRAL View of Sgr B2
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IBIS (18-60 keV)
INTEGRAL detects hard X-ray emission from Sgr
B2 (Revnivtsev
(Revnivtsev et al. 2004)
First detection of a molecular cloud above 20 keV
Composite light curve from ASCA, BeppoSAX,
BeppoSAX,
Chandra, and XMM shows constant 6.4 keV line
flux from 1993-2000
BeppoSAX catalog of bright X-ray sources near
GC have 2-10 keV Lx ~ 1-4x1036 erg s-1 and are
generally stable
Composite X-ray Spectrum of Sgr B2
Best-fit X-ray reflection model to
ASCA, GRANAT, and INTEGRAL
spectrum of Sgr B2
Continuum photon index is 1.8 +/0.2 (typical AGN or XRB spectrum)
IBIS hard bandpass eliminates
possibility of a hidden local irradiator
in or behind Sgr B2
Cosmic ray excitation requires ~1040
erg s-1 ~ Lbol ~ LIR (produced by hot
stars)
Revnivtsev et al. suggest Sgr A*
was a low luminosity AGN Lx ~
1.5x1039 erg s-1 (2-200 keV) about
300-400 yr ago
Reflections of Sgr A*’s Past
as an AGN
X-ray: Fe 6.4 keV
10 pc
Murakami et al. (2001); Park et al. (2004);
Muno et al. (2007); Koyama et al. (2007)
Morphological Variability of Fe
Fluorescence Features
• Features are ~1’ (2 pc) long and
~0.3’ (0.7 pc) long
• Intensity and morphology of
fluorescent Fe lines change on
timescales of 2-3 yr
• Rapid variability precludes origin by
keV electrons (v ~ 0.6c) interacting
with molecular gas (Valinia et al.
2000, Yusef-Zadeh et al. 2002)
• Argues against motion of Fe-rich
SN ejecta (Bykov 2002)
• Pc scales require X-ray irradiator
>~1038 erg/s with 2-3 yr duration
Muno et al. (2007)
X-ray Spectra of Fluorescence Features
Assumed identical ISM
absorption and continuum shape
for both features at all epochs
Best-fit photon index is 1.8 +/0.13, consistent with continuum
of Sgr B2 irradiator
Supports recent claim made for
Sgr B2 by Revnivtsev et al.
(2004)
Continued deep monitoring may
reveal direction of propagation
Arguments Against Local X-ray Irradiators
• Unusual for an XRB to be in outburst for so long (Chen et al. 1997).
• Microquasars and some pulsars might have required luminosity
and hard spectrum in high state
• Fluorescent line seen in Sgr B2, Sgr C, and central parsecs of
Galaxy, so would need multiple microquasars, such as GRS
1915+10, but none of them would currently be bright.
• Need sources that are bright for years and then shut off completely
for years.
• Circinus X-1 dims for only 5 of its 16-day period; it never really
shuts off.
• No X-ray satellite has seen these hypothetical microquasars turn
on or off.
• Irradiation by a single source, Sgr A*, provides simpler explanation.
Reflections of Sgr A*’s Past
as an AGN
Carbon I (492 GHz)
Magnetic Filaments
Radio: 6,20,90 cm VLA
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Radio images of the Galactic center show numerous
“filaments”, powered by synchrotron emission from
relativistic electrons spiraling along mGauss magnetic fields
(Yusef-Zadeh & Morris 1987).
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The origins of these electrons and magnetic fields is a
matter of debate:
• Are the fields pervasive through the Galactic center (Morris & Serabyn
1996)?
• Are the fields and particles both enhanced locally, by young stars or
supernova (LaRosa et al. 2005; YusefYusef-Zadeh et al. 2005)?
Magnetic Filaments
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There are X-rays from a few filaments (e.g., Lu et al. 2003), but
• The X-rays don’t extend the length of the radio filament.
• Most equally-bright filaments show no X-rays.
X-ray: 4-6 keV continuum
Magnetic Filaments
Radio: 20 cm VLA
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Perhaps it is regions of hot plasma that
compress the filaments.
X-ray: He-like S
Conclusions
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Appear to have found all active transients in the field
Looks like GC may be a LMXB factory
We have ~20 potential quiescent HMXBs candidates,
and will have many more in near future
Find large number of wind-driven massive star
binaries associated with active star formation regions
X-ray line maps provide new views of star formation
and allow us to piece together some dynamics
Sgr A*’s reflections associated with diffuse clouds
No constraints on the magnetic filaments as yet!
THE END
Sulfur 1.8 kev
Silicon 2.5 kev
Iron K 6.4 kev
8 um
5.8 um
3.6 um
Sulfur 1.8 kev
Silicon 2.5 kev
Iron K 6.4 kev
330 MHz
1.4 GHz
8 um
Dual-colour imaging:
Investigate the variation of dust properties on large
scales
450μm
SCUBA F-O-V
SCUBA-2 F-O-V
850μm
SCUBA Survey of the Galactic Centre (Pierce-Price et al. 2000)
Maximum mapping speed: Unbiased surveys of
the Galaxy
Our global picture of Galactic star formation
is based on the study of only a few
molecular clouds (e.g. Orion or Galactic
Centre).
SCUBA Galactic Centre Survey
~ 15 shifts (or 120 hrs)
of telescope time
SCUBA-2 will allow a complete census of
giant molecular clouds, star-forming
regions, protostars and pre-stellar cores.
SCUBA-2 field in same integration time The first submillimetre Galactic PLANE Survey?
SCUBA F-O-V
SCUBA-2 F-O-V
850μm
SCUBA Survey of the Galactic Centre (Pierce-Price et al. 2000, ApJ 545, L121)
Outline
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Properties of the Galactic supermassive black
hole: Sagittarius A*
• Fe Ka fluorescence in the molecular cloud Sgr B2
• ASCA
• INTEGRAL
• Chandra detection of variable Fe fluorescence
features within 6’ (14 pc projected) of Sgr A*
• Thomson scattering constraints on the luminosity
of Sgr A* in the past 104 to 105 yr
X-ray Emission-Line Equivalent-Width Maps
Park et al. 2004
Fe He
Fe K “neutral”
(E ~ 6.7 keV)
(E ~ 6.4 keV)
S He + Ly
Si He
(E ~ 2.5 keV)
(E ~ 1.8 keV)
and S Overplotted with CS
Contours
Fe 6.4 keV
S
Light Echoes from a Past Outburst
of Sgr A*?
Muno et al. (2007)
Luminosity Constraints from Thompson
Scattering off Molecular Clouds
• Cramphorn & Sunyaev (2002) used
ASCA observations of known
molecular clouds to constrain the
X-ray luminosity of Sgr A* in the
past
• At times during last 4x104 yr, Lx <
8x1040 erg s-1
• At other times during last 4x104 yr,
Lx < 1041 - 1042 erg s-1
• CO data insensitive to enhanced
activity 8,000 and 14,000 yr ago
for a few 103 yr
• During last 4x104 yr, Lx < 1042 erg s1 for flares with durations > 3,000
yr since they fill the gaps
Luminosity Constraints from Thomson
Scattering Off H I in the Disk
• Typical H I cloud mass <~
104 Msun with ~ 300 lt-yr
separation
• During last 8x104 yr, Lx <
few 1042 erg s-1 (1% LEdd)
for durations > 1000 yr
• During last 105 yr, Lx <
few 1044 erg s-1 (LEdd) for
durations > 1000 yr
Not So Long Ago, in a Galaxy
Not So Far Away…
Sgr A* currently has a quiescent X-ray luminosity of ~2x1033
erg s-1 or ~10-10 Ledd
Flares daily by 10-100x for <~ few hrs
Fluorescent Fe features in the central 6’ suggest Sgr A* may
have been >~ 1038 erg s-1 for at least 2-3 yr about 60 yr ago,
before the first X-ray satellites were launched; however an Xray binary origin is still possible; proper motion key test!
Sgr B2 fluorescence indicates Sgr A* may have been as
luminous as a few 1039 erg s-1 for at least 20-30 yr about 300400 yr ago
Constraints from Thomson scattering off of molecular clouds
and neutral hydrogen indicate that Sgr A* has been less than
1% Ledd during the past 104 yr and less than LEdd for the past
105 yr for outbursts lasting 1000 yr or more